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New Member

Gratuitous ARP Problem

Hi,

We’ve recently experienced arp issues on our core switches when our F5 load balancers failover. We have one F5 load balancer at each of our data centres which are connected via layer 2 dark fibre links.

When the F5 load balancers failover they send out a gratuitous arp broadcast. The servers behind the load balancer update their arp cache during failover but our core Cisco 6500 and Nexus switches don’t. To resolve the issue I have to clear the arp cache on all 4 core switches.

Can anything be changed on the switches so they update the arp cache during these arp broadcasts.

Thanks

Darren

7 REPLIES
Silver

Gratuitous ARP Problem

Darren,

Do you have F5 and servers on the same subnet? If so, switches need not have ARP entry for LBA.

Thanks.

New Member

Gratuitous ARP Problem

Hi,

At the back end the servers are on the same subnet as the F5 device but the failover at this end worked OK. The problem was the vlan which is used for the virtual ip addresses. When this failed over our core switches didn't  update arp cache.

Thanks

Darren

Silver

Gratuitous ARP Problem

I think you mean to say south switches failovered fine but north switches didn't. When F5 failovers, the whole box failovers. You can tcpdump on the north side interface and see if gratuitous arp was sent.

Thanks.

New Member

Gratuitous ARP Problem

Hi,

the 6500's arp expire time is 300 by default, when the time is expire, the switch can update the ARP entry in the ARP table.

To solve your question, you can configure thestatic MAC address in your F5,

Network-》VLANS-》configuration:advanced-》MAC Masquerade

if so ,when the active F5 down, the standby F5 can take the active role without send the gratuitous ARP packet.

Silver

Gratuitous ARP Problem

Is this something that happens all the time? This link may be helpful.

Thanks.

New Member

Gratuitous ARP Problem

Thanks, all replies very helpful.

New Member

Hi,Can you share what the

Hi,

Can you share what the resolution was for this issue?

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